1. Field of the Invention
This invention relates to semiconductor laser diodes, which can emit light in the visible short wavelength spectrum of light, particularly in the blue to violet and also in the ultraviolet region.
2. Description of the Prior Art
Presently used shortest wavelength current injection semiconductor laser diodes are produced from indium gallium aluminum phosphide (InGaAlP) group crystals. Their emission wavelengths are limited to the visible long wavelength region, i.e., a red region of 0.6 to 0.7 micrometers.
However, the physical properties of such material makes difficult the formation of semiconductor laser diodes which can emit light having a shorter wavelength region, i.e., in the blue and violet region or ultraviolet region of light. To overcome these deficiencies it becomes necessary to design laser diodes made from semiconductor materials having broader band gap energies. A typical such candidate material is (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y N.
Recent studies confirm (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y N, particularly GaN, is capable of st emission by photo-excitation at room temperature (300.degree.K.) (see H. Amano et al, Japanese Journal of Applied Physics, Vol. 29, 1990, 1205-L206). Therefore, attempts have been made to produce a laser diode using this material.
Until recently, formation of a P-type single crystal thin film has been difficult to obtain and a current injection semiconductor laser diode using (Al.sub.x Ga.sub.1-x).sub.y In.sub.1-y N has not been achieved.